Since plastics are generally molded easily as compared with glass and metals and can be easily molded into various shapes, they are used for various purposes. Among them, the package field of containers such as bottles and caps attached to containers is the typical application field of plastics.
By the way, when a liquid is contained in the above container, there is always a dripping problem and a device which prevents the liquid from dripping along the outer wall of the mouth portion of the container when the liquid contained in the container is poured out from the mouth portion is required.
According to the type of the liquid in contact with the surface of the container, there is also a liquid adhesion problem. For example, in a container for containing a highly viscous liquid, the liquid adheres to the inner wall of the container, thereby causing a problem with the dischargeability of the liquid from the container. That is, even when the container is inclined, the liquid is not discharged smoothly (low drop-off properties) or it is difficult to discharge all the amount of the liquid in the container, whereby a considerable amount of the liquid remains in the container. Therefore, means for suppressing liquid adhesion to the surface is required.
To prevent liquid dripping and liquid adhesion, liquid repellency should be provided to enhance slipping properties for a liquid on the surface of a plastic molded body, and it is conceivable that to improve liquid repellency, a fluorine-containing resin such as polytetrafluoroethylene is used as a plastic. However, as the fluorine-containing resin is very expensive and difficult to be molded, its use is greatly limited. Therefore, it is desired that the liquid repellency of a plastic molded body formed by using a non-fluororesin containing no fluorine such as a polyolefin or polyester should be improved.
In general, to improve liquid repellency, means for forming a liquid repellent film on the surface and means for forming irregularities on the surface are typical, and means combining them has recently been proposed.
That is, means for forming a liquid repellent thin film (for example, a film comprising a compound or resin containing fluorine or silicon) on the surface is to prevent liquid dripping or liquid adhesion by making a liquid repellent substance existent on the surface. In this means, there is limitation to liquid repellency, for example, liquid repellency is not satisfactory in terms of improving slipping properties for a liquid so that liquid dripping cannot be effectively prevented or the liquid drop-off properties are not fully enhanced. Since it is difficult to form a film which is uniform in thickness, liquid repellency is apt to vary.
The means for forming irregularities on the surface is to physically provide liquid repellency by surface shape. That is, when a liquid flows over an irregular surface, airs pockets are formed in concave portions, the contact state between the irregular surface and the liquid becomes solid-liquid contact and gas-liquid contact, and a gas (air) is a most hydrophobic substance. Therefore, by suitably setting the crude density of irregularities, extremely high liquid repellency is developed, thereby making it possible to improve drainability, prevent liquid dripping effectively and further improve liquid drop-off properties effectively. However, even in this means, when the liquid flows over the irregular surface repeatedly, the liquid gradually accumulates in the concave portions, and air pockets are gradually lost with the result that drainability and liquid drop-off properties gradually deteriorate.
In recent years, technology which combines the above means for making a liquid repellent substance existent on the surface and the above means for forming irregularities on the surface has been proposed. That is, the technology aims to effectively avoid inconvenience that the liquid accumulates in the concave portions by making the liquid repellent substance existent on a surface having irregularities, thereby maintaining liquid repellency for a long period of time.
For example, Patent Document 1 proposes the production of a water- and oil-repellent film by forming an inorganic hard film such as a silicon oxide film on the surface of a plastic film, making fine irregularities on this surface and forming a chemisorption monomolecular film containing fluorine on the irregular surface by using a compound containing a hydrocarbon fluoride group and a chlorosilyl group.
Patent Document 2 proposes a water- and oil-repellent resin molded body having fine irregularities on the surface of a resin molded body containing a fluoroalkyl-based surfactant having water- and oil-repellency.
However, even the above Patent Documents 1 and 2 do not succeed in maintaining drainability and liquid drop-off properties stably.
For example, in Patent Document 1, the chemisorption monomolecular film containing fluorine is gradually removed by bringing it into contact with a liquid repeatedly, whereby the liquid gradually accumulates in the concave portions, thereby gradually losing drainability and liquid drop-off properties.
In Patent Document 2, since the fluoroalkyl-based surfactant bleeds out onto the surface, water repellency and liquid repellency are developed. However, when the liquid is brought into contact with the surface repeatedly, the bleeding fluoroalkyl-based surfactant is gradually removed with the result that drainability and liquid drop-off properties gradually deteriorate.
Further, the inventors of the present invention previously proposed a plastic molded body having a fractal hierarchical surface irregular structure that primary irregularities are formed on the surface and secondary fine irregularities are formed on at least some of the primary irregularities (JP-A 2013-220998).
As secondary finer irregularities are formed within the area of the primary irregularities in this molded body, the entry of a liquid into the primary irregularities is effectively suppressed, and liquid repellency obtained by the primary irregularities is maintained stably.
However, even this means has limitation to the suppression of the deterioration of drainability and liquid drop-off properties. That is, the entry of the liquid into the secondary irregularities cannot be prevented completely, drainability and liquid drop-off properties obtained by the air pockets formed in the secondary irregularities gradually deteriorate, and therefore the liquid gradually enters the primary irregularities with the result that the deterioration of drainability and liquid drop-off properties cannot be avoided.
Even when the molded body is brought into contact with a liquid repeatedly, drainability and liquid drop-off properties must be maintained stably.